Bulletin / Cutting edge
Fast-spinning asteroid sends plumes of particles into space
is proving to be an enigmatic body for planetary scientists exploring with NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identifcation, Security-Regolith Explorer) spacecraft. They have discovered that it is ejecting plumes of particles from the surface into space.
The frst close-up pictures revealed the asteroid’s surface is littered with rocks and boulders, leaving mission planners struggling to fnd a spot to touch down next year and take a sample to return to Earth in 2023. But the ejection of jets of particles, observed since early January, was completely unexpected.
“The discovery of plumes is one of the biggest surprises of my career,” says principal investigator Dante Lauretta, of the University of Arizona.
Some particles were observed to orbit Bennu as satellites before falling back to the surface. None of the plumes are seen as a threat to the probe as it orbits at a distance of around 1.6km.
The ejected plumes are unlike those from comets as they are warmed by the Sun. A clue to their cause may come from the balance that exists between Bennu’s weak gravitational pull and its spin, which gives rocks enough energy to escape into space. “When you spin this guy up, you create a competition between the gravity that’s holding you down and the centrifugal acceleration, which is trying to throw you off,” says Daniel Scheeres, of the mission’s radio science team at the University of Colorado Boulder.
Bennu’s orbit brings it close to Earth as a potentially hazardous object. Dust particles ejected in the past may even produce a minor meteor shower.
NASA’s OSIRIS- REx has discovered particles being ejected from asteroid Bennu, and inset, its rocky surface